Communication apparatus, communication system, and communication controlling method to synchronize clock process

ABSTRACT

Techniques for synchronizing a clock of a first apparatus and a clock of a second apparatus in communication with the first apparatus via a network. The techniques include communicating first data between the first apparatus and second apparatus via a network, communicating, while at least a portion of the first data is being communicated via the network, a synchronization packet between the first apparatus and the second apparatus, and communicating second data between the first apparatus and the second apparatus after synchronization between the first apparatus and the second apparatus has been established.

TECHNICAL FIELD

The present disclosure relates to a communication apparatus, acommunication system, a communication controlling method, and a program.In particular, the present disclosure relates to a communicationapparatus, a communication system, a communication controlling method,and a program that execute a clock synchronizing process betweenmultiple apparatuses connected to each other via a network.

BACKGROUND ART

For example, if contents used for a television broadcast are generated,a process that generates the contents used for the broadcast is executedby transmitting images captured by multiple video cameras disposed atmultiple different positions are transmitted to an editing studio via anetwork, and by executing an editing process which generates an image orthe like in which multiple images are combined or one image is selectedfrom images captured by multiple cameras in an editing apparatus in theediting studio.

In such an editing process, it is necessary to exactly discriminate whattiming each image is captured individually by each camera. Asinformation for this, a time stamp indicating a capturing time or thelike is set in the image captured by each camera, and the editingapparatus executes the editing process with reference to the time stamp,thereby enabling the image captured by each camera to be edited withoutany time difference.

However, the time stamp is set by using a clock signal generated by aclock embedded in each apparatus connected via a network. If there is aphase difference or a frequency difference in the clock signal ofapparatuses connected via the network, a difference occurs in the timestamp set in each apparatus.

In order to correct the clock signal difference between apparatusesconnected via the network, a clock synchronizing process which transmitsand receives a synchronization packet between the devices connected viathe network is executed. For example, PTL 1 (Japanese Unexamined PatentApplication Publication No. 2010-190635) in the related art disclosesthe synchronizing process between multiple communication apparatusesconnected via a packet transmission network such as Ethernet (aregistered trademark).

PTL 1 discloses a configuration where the clock synchronizing process isexecuted between a master and a slave by transmitting and receiving apacket between a master apparatus and a slave apparatus that execute thesynchronizing process, and performing an analysis to which transmissiontime information and reception time information which are recorded inthe received packet is applied.

However, in a communication process via the network, a communicationdelay occurs. This delay amount is not constant and varies depending onnetwork load situations. In other words, jitter which is a fluctuationof delay time occurs. For example, the synchronizing process bysynchronization packet transmission and reception such as that describedin the above-described PTL 1 can be executed with high precision whenthe network delay is constant, but when such jitter occurs, there is aproblem that it is difficult to execute a highly precise synchronizingprocess.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2010-190635

SUMMARY Technical Problem

It is desirable to provide a communication apparatus, a communicationsystem, a communication controlling method, and a program that enable anefficient clock synchronizing process to be executed between multiplecommunication apparatuses. In addition, it is desirable to provide acommunication apparatus, a communication system, a communicationcontrolling method, and a program that enables communication of actualdata such as image data to be started between the communicationapparatuses that have established early synchronization by completingthe clock synchronizing process in a short time when a system isactivated, for example.

Solution to Problem

Accordingly, some embodiments are directed to a first apparatus. Thefirst apparatus comprises at least one processor programmed tocommunicate first data between the first apparatus and second apparatusvia a network. The at least one processor further being programmed tocommunicate, while at least a portion of the first data is beingcommunicated via the network, a synchronization packet between the firstapparatus and the second apparatus, and communicate second data betweenthe first apparatus and the second apparatus after synchronizationbetween the first apparatus and the second apparatus has beenestablished.

Other embodiments are directed to a first apparatus. The first apparatuscomprises a network interface configured to communicate with a secondapparatus via a network, and at least one processor. The at least oneprocessor is programmed to transmit first data to the second apparatusvia the network interface, communicate, while at least a portion of thefirst data is being transmitted, a synchronization packet between thefirst apparatus and the second apparatus via the network interface, andtransmit second data to the second apparatus after synchronizationbetween the first apparatus and the second apparatus has beenestablished.

Still other embodiments are directed to a first apparatus. The firstapparatus comprising a network interface configured to communicate witha second apparatus via a network, and at least one processor. The atleast one processor is programmed to receive, via the network interface,first data sent from the slave apparatus, communicate, while at least aportion of the test data is being received via the network interface, asynchronization packet between the first apparatus and the secondapparatus, and receive second data from the second apparatus aftersynchronization between the first apparatus and the second apparatus hasbeen established.

Still other embodiments are directed to a method of synchronizing aclock of a first apparatus and a clock of a second apparatus incommunication with the first apparatus via a network. The methodcomprises transmitting first data from the first apparatus to the secondapparatus via the network, communicating, while at least a portion ofthe first data is being transmitted, a synchronization packet betweenthe first apparatus to the second apparatus via the network, andtransmitting second data from the first apparatus to the secondapparatus after synchronization between the first apparatus and thesecond apparatus has been established.

Still other embodiments are directed to a method of synchronizing aclock of a first apparatus and a clock of a second apparatus incommunication with the first apparatus via a network. The methodcomprises receiving, by the first apparatus, first data sent from thesecond apparatus via the network, communicating, while at least aportion of the first data is being received, a synchronization packetbetween the first apparatus and the second apparatus via the network,and receiving second data from the second apparatus aftersynchronization between the first apparatus and the second apparatus hasbeen established.

Furthermore, for example, the program of the present disclosure is theprogram that can be provided by a storage medium and a communicationmedium provided in a computer-readable form, with respect to aninformation processing apparatus or a computer system that can executevarious program codes. Such a program is provided in thecomputer-readable form, and thereby the process according to the programon the information processing apparatus or the computer system may berealized.

Still other object, features or advantages of the present disclosurewill become apparent by a detailed description with reference to theattached drawings and the embodiments of the present disclosuredescribed below. Furthermore, the system in the present specification isa logical collection configuration of multiple apparatuses, and theapparatuses with the respective configurations are not all limited to beaccommodated in the same housing.

Advantageous Effects of Invention

According to the configuration of the embodiments of the presentdisclosure, an efficient clock synchronizing process is realized betweencommunication apparatuses via a network. Specifically, the clocksynchronizing process is executed as follows between a firstcommunication apparatus and a second communication apparatuscommunicating with each other via the network. In other words, the firstcommunication apparatus executes the clock synchronizing processaccompanied by a synchronization packet transmission and reception withthe second communication apparatus during a non-transmission period ofactual data such as image contents scheduled to be transmitted to thesecond communication apparatus. The second communication apparatusexecutes the clock synchronizing process to which the synchronizationpacket is applied during a non-reception period of the actual data, andtransmits a notification packet denoting synchronization establishmentto the first communication apparatus after synchronization isestablished. The first communication apparatus starts transmission ofthe actual data such as the image contents with respect to the secondcommunication apparatus according to the notification packet receptionfrom the second communication apparatus. This configuration enables thesynchronizing process to be executed in a stable situation with lessnetwork load and less network delay fluctuation (jitter).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrated with regard to a configuration and aprocess of a communication apparatus that executes a clocksynchronization process.

FIG. 2 is a view illustrated with regard to a specific example of theclock synchronization process.

FIG. 3 is a view illustrated with regard to a communication sequence inthe clock synchronizing process executed between the communicationapparatus.

FIG. 4 is a view illustrated with regard to an example of jitter whichis a delay fluctuation of a network.

FIG. 5 is a view illustrated with regard to an example of a variationresulting from a time trend of communication data volume on the network.

FIG. 6 is a view illustrating a flowchart described with regard to anexample of a process sequence of the clock synchronizing processaccording to the present disclosure.

FIG. 7 is a sequence diagram illustrated with regard to an example ofthe process sequence of the clock synchronizing process according to thepresent disclosure.

FIG. 8 is a view illustrating a flowchart described with regard to anexample of the process sequence of the clock synchronizing processaccording to the present disclosure.

FIG. 9 is a view illustrated with regard to an example of a variationresulting from a time trend of transmission data volume in the clocksynchronizing process according to the present disclosure.

FIG. 10 is a view illustrated with regard to a configuration example ofa system which executes the clock synchronizing process according to thepresent disclosure.

FIG. 11 is another view illustrated with regard to the example of avariation resulting from a time trend of the transmission data volume inthe clock synchronizing process according to the present disclosure.

FIG. 12 is a view illustrating a flowchart described with regard to theexample of the process sequence of the clock synchronizing processaccording to the present disclosure.

FIG. 13 is a view illustrated with regard to the example of a variationresulting from a time trend of the transmission data volume in the clocksynchronizing process according to the present disclosure.

FIG. 14 is a view illustrated with regard to an example of a variationresulting from a time trend of the transmission data volume in the clocksynchronizing process according to the present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a communication apparatus, a communication system, acommunication controlling method and a program of the present disclosurewill be described in detail with reference to the drawings. Furthermore,the description will be made according to the following items.

1. With Regard to Summary of Clock Synchronizing Process usingSynchronization Packet

2. With Regard to Jitter in Network Communication

3. With Regard to First Embodiment of Synchronizing Process according toPresent Disclosure

4. With Regard to Second Embodiment of Synchronizing Process accordingto Present Disclosure

5. With Regard to Other Embodiment

6. Summary of Configuration of Present Disclosure

1. With Regard to Summary of Clock Synchronizing Process UsingSynchronization Packet

First, the summary of the clock synchronizing process using thesynchronization packet will be described. Hereinafter, a clocksynchronization sequence specified in IEEE1588 will be described as anexample of the clock synchronizing process using the synchronizationpacket.

FIG. 1 illustrates a master apparatus 110 and a slave apparatus 120 astwo apparatuses which execute the clock synchronization process. Themaster apparatus 110 and the slave apparatus 200 transmit and receive apacket via an IP communication network such as Ethernet (a registeredtrademark) which is an asynchronous transmission network. For example,one specific example is that the slave apparatus 120 is a video cameraand the master apparatus 110 is an editing apparatus which performs anediting process by receiving an image of the video camera.

The master apparatus 110 includes a master clock 111, a counter 112, adata processing unit 113 and a communication unit 114. The master clock111 generates a master clock signal (Mclk) 115 and outputs the generatedclock signal to the counter 112. The counter 112 generates a countervalue based on the master clock signal (Mclk) 115 input from the masterclock 111 and outputs the counter value to the data processing unit 113.

The data processing unit 113 inputs the counter value generated by thecounter 112 and executes various data processes based on the countervalue. For example, the data processing unit 113 executes a process forthe clock synchronization process, further the process depending on theapparatus, an acquisition process of video camera capturing data if themaster apparatus 110 is the video camera, for example, a time stampsetting process based on the counter value, or the like. In addition, ifthe master apparatus 110 is the editing apparatus which edits contentsreceived from a slave apparatus which is the video camera, the masterapparatus 110 executes a content editing process or the like using thetime stamp set in the content.

For example, the data processing unit 113 is configured by a CPU havinga program execution function, a memory which stores the program, data,various parameters or the like, or the like. The communication unit 114executes a packet transmission and reception with the slave apparatus120.

The slave apparatus 120 includes a slave clock 121, a counter 122, adata processing unit 123 and a communication unit 124. The slave clock121 generates a slave clock signal (Sclk) 125 and outputs the generatedclock signal to the counter 122. The counter 122 generates a countervalue based on the slave clock signal (Sclk) 125 input from the slaveclock 121 and outputs the counter value to the data processing unit 123.

The data processing unit 123 inputs the counter value generated by thecounter 122 and executes various data processes based on the countervalue. For example, the data processing unit 123 executes the processfor the clock synchronization process, further the process depending onthe apparatus, the acquisition process of the video camera capturingdata if the slave apparatus 120 is the video camera, for example, thetime stamp setting process based on the counter value, or the like. Inaddition, if the slave apparatus 120 is the editing apparatus whichedits contents receiving from the slave apparatus which is the videocamera, the master apparatus 110 executes the content editing process orthe like using the time stamp set in the contents.

For example, the data processing unit 123 is configured by the CPUhaving the program execution function, the memory which stores theprogram, the data, the various parameters or the like. The communicationunit 124 executes the packet transmission and reception with the masterapparatus 110.

Here, the clock signal (Mclk) generated by the master clock 111 in themaster apparatus 110 and the clock signal (Sclk) generated by the slaveclock 121 in the slave apparatus 120 are not limited to be synchronizedwith each other. In other words, in general, a frequency difference or aphase difference occurs as illustrated in FIG. 2.

When data communication is executed between the master apparatus 110 andthe slave apparatus 120 which have such unsynchronized clocks, there isa case where the clock synchronizing process has to be executed. Inother words, in a case where the data editing or the like is executedbased on the time stamp described above, the clock synchronization isdesired.

In the clock synchronization process, there are various methods, but,for example, there is one clock synchronization processing sequencespecified in IEEE 1588. Hereinafter, the clock synchronizationprocessing sequence in the IEEE1588 will be described. In the clocksynchronization according to the IEEE1588 sequence, the master apparatus110 transmits a PTP (Precision Time Protocol) message to the slaveapparatus 220.

For example, the PTP message is a message packet containing messagetransmission time information or the like. Furthermore, for example, thetime information uses a value in which the counter value set by thecounter 112 of the master apparatus 110 is converted into a nano second(ns: nano second) unit value that is the time information. Because ofthe converting process, the data processing unit 113 of the masterapparatus 110 includes a function which converts the counter value intothe time information value of the nano second (ns) unit.

In a synchronization packet transmitting process of one unit, thefollowing messages, in other words, a synchronization message (Sync) anda delay response message (DelayResponse) are included in the PTP messagethat the master apparatus 110 transmits to the slave apparatus 120.

The synchronization message (Sync) is a message which contains the timeinformation for executing the time synchronization. The master apparatus110 continuously transmits multiple synchronization messages (Sync).Furthermore, there is a case where the synchronization message (Sync)subsequent to a preceding synchronization message (Sync) is called afollow-up message. The delay response message is a message transmittedas a response after a delay request (DelayRequest) message is receivedfrom the slave apparatus 220, and a message which contains receptiontime information on the delay request (DelayRequest) message receivedfrom the slave apparatus 220.

The slave apparatus 120 receives the PTP message from the masterapparatus 110 and transmits the PTP message generated by the slaveapparatus 120 to the master apparatus 110. The PTP message which theslave apparatus 120 transmits to the master apparatus 110 is the delayrequest (DelayRequest) message. The delay request message is transmittedto the master apparatus 110 in order to request the delay requestmessage, after the synchronization message (Sync) is received from themaster apparatus 210.

FIG. 3 is a sequence diagram illustrating the clock synchronizationprocessing sequence between the master apparatus 110 and the slaveapparatus 120 illustrated in FIG. 1. Each process of steps S101 to S108will be described.

(Step S101)

A first synchronization message (Sync(t11)) is transmitted from themaster apparatus 110 to the slave apparatus 220. A transmission time t11of the first synchronization message is contained in the firstsynchronization message (Sync (t11)). This is the time information(t11(M)) on the master clock (Mclk) base. Hereinafter, in each timeinformation (txy), (M) is additionally described in the time informationin which the master clock is measured as a reference clock, and (S) isadditionally described in the time information in which the slave clockis measured as the reference clock.

(Step S102)

The slave apparatus 120 receives the first synchronization message(Sync(t11(M))) transmitted from the master apparatus 110, and recordsmessage transmission time information (t11(M)) contained in the receivedfirst synchronization message (Sync (t11(M))) and the message receptiontime, in other words, reception time information (t21(S)) on a slaveclock (Sclk) base, in the memory.

(Step S103)

A second synchronization message (Sync(t12(M))) is further transmittedfrom the master apparatus 110 to the slave apparatus 220. A transmissiontime t12 of the second synchronization message is also contained in thesynchronization message (Sync(t12(M))). This is the time information(t12(M)) on the master clock (Mclk) base.

(Step S104)

The slave apparatus 120 receives the second synchronization message(Sync(t12(M))) transmitted from the master apparatus 110, and recordsmessage transmission time information (t12(M)) contained in the receivedsynchronization message (Sync(t12(M))) and the message reception time,in other words, reception time information (t22(S)) on the slave clock(Sclk) base, in the memory.

(Step S105 a and 105 b)

Next, the delay request message (DelayRequest) is transmitted from theslave apparatus 120 to the master apparatus 110. The slave apparatus 120records an issue (transmission) time t31(S) of the delay request messagein the memory as time information (t31(S)) on a slave clock (Sclk) base.

(Step S106)

The master apparatus 110 receives the delay request message transmittedfrom the slave apparatus 120, and records a reception time t41(M) of thedelay request message, in other words, time information (t41(M)) on themaster clock (Mclk) base, in the memory.

(Step S107)

Next, the delay request message (DelayRequest) is transmitted from themaster apparatus 110 to the slave apparatus 120. A reception time t41 ofthe above-described delay request message, in other words, the timeinformation (t41(M)) on the master clock (Mclk) base is contained in thedelay response message.

(Step S108)

The slave apparatus 120 receives the delay request message transmittedfrom the master apparatus 110, obtains the reception time t41(M) of thedelay request message, in other words, the time information (t41(M)) onthe master clock (Mclk) base, and records that in the memory.

The following items of time information are recorded in the memory ofthe slave apparatus 120 by the associated process.

(1) t11(M): the time information on the master clock (Mclk) baseindicating the transmission time of the first synchronization message,

(2) t21(S): the time information on the slave clock (Sclk) baseindicating the reception time of the first synchronization message,

(3) t12(M): the time information on the master clock (Mclk) baseindicating the transmission time of the second synchronization message,

(4) t22(S): the time information on the slave clock (Sclk) baseindicating the reception time of the second synchronization message,

(5) t31(S): the time information on the slave clock (Sclk) baseindicating the transmission time of the delay request message,

(6) t41(M): the time information on the master clock (Mclk) baseindicating the reception time of the delay request message,

The data processing unit 123 in the slave apparatus 120 calculates afrequency difference (drift) and a phase difference (offset) between themaster clock signal (Mclk) generated by the master clock 111 in themaster apparatus 110 and the slave clock signal (Sclk) generated by theslave clock 121 in the slave apparatus 120 by applying the pieces oftime information, and executes the clock synchronizing process based onthe calculated the frequency difference (drift) and the phase difference(offset).

Specifically, for example, the data processing unit 123 in the slaveapparatus 120 outputs a correction signal to the counter 122, andcorrects the counter value based on the slave clock signal (Sclk)generated by the slave clock 121 so as to be the same as the countervalue based on the signal synchronized to the master clock. By thisprocess, a difference between the slave clock 121 and the master clock111 is corrected, and the synchronization is established.

Furthermore, the processes of steps S101 to S108 illustrated in FIG. 3illustrate one unit of process sequence in a synchronizing processalgorithm, during an execution period of the communication process, theprocesses of steps S101 to S108 are repeatedly executed, and the processwhich maintains synchronization of each communication apparatus isexecuted between actual communication apparatuses. For example, withrespect to a slave from a master, synchronization message packets of 64packets per second are continuously transmitted, and the process whichmaintains the synchronization between two communication apparatuses (themaster and the slave) is executed by the control process using thepackets.

Furthermore, in the synchronizing process executed by the dataprocessing unit 123 in the slave apparatus 120, for example, thefollowing process is executed. The data processing unit 123 generates acontrol voltage depending on a difference amount between the slave clock121 and the master clock 111, outputs the control voltage to a VCO(Voltage Controlled Oscillator), and inputs the VCO output to thecounter 122, thereby executing a servo process or the like, in otherwords, performing a PID control of a count process of the counter 122.

Furthermore, the frequency difference (drift) and the phase difference(offset) are calculated according to the following calculation equations(Equation 1) and (Equation 2).frequency drift (drift)=(t12(M)−t11(M))−(t22(S)−t21(S))  (Equation 1)phase offset (offset)={(t22(S)−t12(M))−(t41(M)−t31(S))}/2  (Equation 2)

The data processing unit 123 in the slave apparatus 120 calculates thefrequency difference (drift) and the phase difference (offset) betweenthe master clock (Mclk) and the slave clock (Sclk) according to thecalculation equations (equation 1) and (equation 2), and generates thecorrection signal based on the calculation result. The correction signalis input to the counter 122, and the counter value generated on thebasis of the slave clock (Sclk) is controlled, and thereby thesynchronization process is executed. Furthermore, the synchronizingprocesses are continuously executed during the data communication periodbetween the master and the slave.

2. With Regard to Jitter in Network Communication

As described above, the synchronizing process between the communicationapparatuses connected to each other via the network is executed by thetransmission and reception of multiple message packets such as thesynchronization message via the network.

However, in the communication via the network, delay occurs due tovarious factors. A delay amount varies depending on a network situation,for example, an increased or decreased communication load. In otherwords, in the network communication, a fluctuation of the delay amount,so-called jitter (Jitter) occurs. The synchronizing process by thesynchronization packet transmission and reception is executed withoutany problem when the communication delay is constant without such jitter(Jitter), but when jitter (Jitter) occurs, it is difficult to execute aprecise synchronization process.

FIG. 4 is a view illustrating a concept of time variation of the jitter.A horizontal axis indicates the time and a vertical axis indicates thejitter. In other words, the variation resulting from the time trend ofthe network delay amount is illustrated. As illustrated in FIG. 4, thedelay amount of an IP network which is an asynchronous transmissionnetwork varies moment to moment.

A main factor of the network delay is an increase and decrease of thedata transmission amount via the network. For example, when an image andaudio data obtained by a capturing process of the video camera aretransmitted via the network, compression data is generated by executinga coding process such as MPEG coding according to a predeterminedalgorithm, and the process that transmits the generated compression datais executed. The data mount of the data generated by the compressionprocess significantly varies depending on a complexity degree of theimage which is subject to compression process. As a result, thetransmission data volume per unit time, specifically, a transmission bitamount (bps) per unit time significantly varies with the elapse of time.Specifically, as shown in a graph of FIG. 5, for example, the datatransmission rate varies with the elapse of time.

FIG. 5 is the graph illustrating time denoted on the horizontal axis andthe data transmission rate (bps) denoted on the vertical axis. If suchtransmission rate varies with the elapse of time, the fluctuation(jitter) of the above-described network delay is likely to occur. Ifjitter occurs, it is difficult to accurately execute the synchronizingprocess accompanied by the synchronization packet transmission andreception previously described, and it causes problems desiring a longtime until a stable synchronization is achieved.

3. With Regard to First Embodiment of Synchronizing Process According toPresent Disclosure

Next, the first embodiment of the synchronizing process according to thepresent disclosure will be described. FIG. 6 is a flowchart illustratinga processing sequence executed in the two communication apparatuseswhich execute the clock synchronization process, for example, the masterapparatus 110 and the slave apparatus 120 illustrated in FIG. 1.

For example, the process according to the flow illustrated in FIG. 6 isexecuted in each data processing unit of the master apparatus 110 andthe slave apparatus 120 illustrated in FIG. 1. For example, the dataprocessing unit of each apparatus obtains the program in which theprocess sequence according to the flow illustrated in FIG. 6 isrecorded, and executes the process by executing the process according tothe obtained program in the CPU of the data processing unit.Hereinafter, the process of each step of the flow illustrated in FIG. 6will be described.

(Step S201)

First, the data processing unit of each communication apparatusexecuting the synchronizing process activates software which is aprogram executing the synchronizing process in step S201.

(Step S202)

Next, in step S202, for example, the data processing unit activates eachapparatus executing the process necessary for executing thesynchronizing process, such as a network processor configuring thecommunication unit.

(Step S203)

Next, in step S203, an activation setting of the network for executingthe communication between the master and the slave is performed.Specifically, the process which enables communication between the masterand the slave, such as a communication setting according to acommunication protocol and a process obtaining a communication address,is executed.

(Step S204)

Next, the transmission and reception process of the synchronizationpacket is started. For example, the process is the synchronizing processaccompanied by the transmission and reception process of each messagepacket between the master and the slave previously described withreference to FIG. 3.

Furthermore, the transmission and reception process of thesynchronization packet in the embodiment to be described later is thetransmission and reception process of the packet necessary for the clocksynchronizing process executed between the master and the slave. Thesynchronization packet is transmitted from the master apparatus to theslave apparatus by setting one apparatus as the master apparatus and theother apparatus as the slave apparatus of the two communicationapparatuses.

For example, when the clock synchronizing process according to theIEEE1588 sequence previously described is executed, the packettransmission and reception process of each PTP message transmitted andreceived between the master and the slave is executed. In this example,as previously described with reference to FIG. 3, for example, thesynchronization packet transmission of 64 packets per one second isperformed from the master apparatus to the slave apparatus.

(Step S205)

The slave apparatus executes the control for synchronizing the clock ofthe master apparatus with the clock of the slave apparatus by using thetime information or the like of the synchronization packet transmittedfrom the master apparatus. This process is executed as the processaccording to the algorithm specified in the IEEE1588, for example, whichis previously described with reference to FIGS. 1 to 3. If it isdetermined that the synchronization is established in the slaveapparatus side, a notification packet denoting the synchronizationestablishment from the slave apparatus to the master apparatus istransmitted. The master apparatus confirms a successful synchronizationestablishment by receiving the notification packet.

If the confirmation is performed, the determination process of step S205is “Yes”, and the process proceeds to step S206.

(Step S206)

In step S205, after the synchronization establishment is confirmed, aprocess is started which transmits actual data to be actuallytransmitted and received between the communication apparatuses, forexample an image and audio as video camera capturing contents, andstream data including other data, for example the stream data in whichthe time stamp of each image unit is set, from one communicationapparatus to the other communication apparatus.

As illustrated in the flowchart, in the process of the presentdisclosure, before starting the transmission and reception of the actualdata to be actually transmitted and received between the communicationapparatuses, such as the image, the audio and the stream data includingother data in step S206, the synchronizing process by the transmissionand reception process of the synchronization packet is executed in stepS204.

In other words, before the actual data transmission in which thevariation of the transmission data volume is expected to occur isstarted, the synchronization packet is transmitted and received betweentwo communication apparatuses (the master and the slave) during anon-transmission period of the actual data, and thereby thesynchronizing process is configured to be executed in a networkenvironment with less jitter. The synchronization packet transmissionand reception is performed in such a stable communication environment,in other words, in a stable network environment with less varied networkdelay amount, thereby enabling a highly precise synchronizing process tobe executed in a short time.

The sequence diagram illustrated in FIG. 7 is a view illustrating a datatransmission and reception sequence between the two communicationapparatuses associated with the present disclosure according to the flowillustrated in FIG. 6.

When the synchronizing process is executed between the communicationapparatuses A and B, the packets transmitted and received between eachof the apparatuses are illustrated.

The communication apparatus A corresponds to the master apparatus andthe communication apparatus B corresponds to the slave apparatus. Insteps S251-1 to S251-n illustrated in FIG. 7, the synchronization packetis transmitted from the communication apparatus A which is the masterapparatus to the communication apparatus B which is the slave apparatus.This process corresponds to the process of step S204 in the flow of FIG.6. The communication apparatus A which is the master apparatuscontinuously transmits the communication packet at a frequency of 64packets per second, for example. The communication apparatus B which isthe slave apparatus receives the synchronization packet, and executesthe synchronizing process by executing the same as the processpreviously described with reference to FIG. 3.

Furthermore, in FIG. 7, even though the packet transmission andreception process of steps S105 and S107 illustrated in FIG. 3 isomitted in FIG. 7, the message packet transmission is appropriatelyexecuted even by the communication apparatus B.

In steps S251-1 to S251-n illustrated in the sequence diagram of FIG. 7,the communication apparatus B which is the slave apparatus receivesmultiple synchronization packets from the communication apparatus Awhich is the master apparatus, and executes the synchronizing process byexecuting the same as the process previously described with reference toFIG. 3. If it is determined that the synchronization is established, thenotification packet for notifying the synchronization establishment instep S252 is transmitted to the communication apparatus A which is themater apparatus.

If the notification packet is received from the communication apparatusB which is the slave apparatus, the communication apparatus A which isthe master apparatus confirms the synchronization establishment, andtransmits the notification packet indicating that the transmission ofthe actual data such as the image data in step S253 is started to thecommunication apparatus B which is the slave apparatus. Further, in step254, the communication apparatus A which is the master apparatus startsthe transmission of the actual data such as image data with respect tothe communication apparatus B which is the slave apparatus.

The processes of steps S252 to S254 correspond to the processes of stepsS205 to S206 in the flowchart illustrated in FIG. 6. Furthermore, thetransmission of the actual data in step S254 is continuously executedthereafter, furthermore, even the transmission and reception of thesynchronization packet is continuously executed in parallel with theactual data delivery. The communication apparatus B which is the slaveapparatus receives the synchronization packet received along with theactual data, continuously executes a synchronization control, andcontinuously executes the control for maintaining the synchronization.

As can be seen from the sequence illustrated in FIG. 7, thesynchronization packet transmission of steps S251-1 to S251-n isexecuted in a stage before the transmission of the actual data such asimage contents are started. Accordingly, the synchronization packettransmission and reception is executed in a stable communicationenvironment with less communication load variation of the network, andthus it is possible to establish efficient synchronization in a shorttime.

4. With Regard to Second Embodiment of Synchronizing Process Accordingto Present Disclosure

Next, the second embodiment of the synchronizing process according tothe present disclosure will be described. FIG. 8 is a flowchartdescribing the processing sequence according to the second embodimentwhich is executed by the two communication apparatuses executing theclock synchronizing process, for example the master apparatus 110 andthe slave apparatus 120 illustrated in FIG. 1.

The process according to the flow illustrated in FIG. 8 is executed ineach data processing unit of the master apparatus 110 and the slaveapparatus 120 illustrated in FIG. 8, for example. For example, theprogram in which the process sequence according to the flow illustratedin FIG. 8 is recorded is obtained from the memory, and the process isexecuted by executing the process according to the obtained program inthe CPU of the data processing unit. Hereinafter, the process of eachstep of the flow illustrated in FIG. 8 will be described.

(Step S301)

First, the data processing unit of each communication apparatus whichexecutes the synchronizing process activates the software which is theprogram executing the synchronizing process, in step S301.

(Step S302)

Next, in step S302, the data processing unit activates each apparatuswhich executes the process necessary for the synchronizing process, suchas a network processor.

(Step S303)

Next, in step S303, the network activation setting for executing thecommunication between the master and the slave is performed.Specifically, the process enabling the communication between the masterand the slave, such as the communication setting according to acommunication protocol and a process obtaining a communication address,is executed. The processes of steps S301 to S303 are executed in thesame processes as steps S201 to S203 of the flow of the first embodimentpreviously described with reference to FIG. 6.

(Step S304)

The process of step S304 is the process which is not included in theflow of the first embodiment previously described with reference to FIG.6. In the second embodiment, test data is transmitted between thecommunication apparatuses in step S304, before the transmission of thesynchronization packet is started in step S305, or along with thestarting of the synchronization packet transmission. For example, thetransmission of the test data including a test image, audio and data isstarted.

(Step S305)

In the present embodiment, the synchronization packet transmission andreception are started along with the test data transmission in stepS305. The process is the synchronizing process accompanied by thesynchronization packet transmission and reception between the master andthe slave previously described with reference to FIG. 3, for example.For example, one apparatus of the two communication apparatuses is setas the master apparatus, and the other apparatus is set as the slaveapparatus, thereby the synchronization packet being transmitted from themaster apparatus to the slave apparatus. As previously described withreference to FIG. 3, for example, the synchronization packettransmission of 64 packets per second is performed from the masterapparatus to the slave apparatus.

In the present embodiment, the synchronizing process accompanied by thesynchronization packet transmission and reception is executed along withthe test data transmission.

This is a measure to avoid a possible synchronization deviation becausethe network load rapidly increases when the actual data is transmitted.

In other words, after a certain situation with a certain degree ofnetwork load is set, the synchronization packet transmission andreception are performed, and the synchronizing process by thesynchronization packet transmission and reception is executed by settingthe situation close to the transmission time of the actual data startedin step S307. Such a process is executed, and thereby it is possible tosuppress the network load from rapidly varying when the actual datatransmission which is started in step S307, and the synchronizationdeviation can be prevented from occurring when the actual datatransmission is started.

(Step S306)

The processes of steps S306 to S307 are the same processes as the stepsS205 to S206 of the flow of the first embodiment previously describedwith reference to FIG. 6. In the step S306, the slave apparatus executesthe control for synchronizing the master apparatus clock with the slaveapparatus clock by using the time information on the synchronizationpacket or the like received from the master apparatus. This process isexecuted as the process according to the algorithm specified in IEEE1588previously described with reference to FIGS. 1 to 3, for example. If itis determined that the synchronization is established in the slaveapparatus side, the notification packet indicating that thesynchronization is established with respect to the master apparatus fromthe slave apparatus is transmitted.

The master apparatus confirms the successful synchronizationestablishment by receiving the notification packet. If the confirmationis performed, the determination process of step S306 is “Yes”, and theprocess proceeds to step S307.

(Step S307)

In step S306, after the synchronization establishment is confirmed, theprocess is started which transmits actual data to be actuallytransmitted and received between the communication apparatuses forexample the image, the audio as video camera capturing contents, and thestream data including other data from one communication apparatus to theother communication apparatus.

As illustrated in the flowchart, in the process of the presentembodiment, the synchronization packet transmission and reception areexecuted in an environment in which the transmission and reception ofthe test data are performed.

With the process, it is possible to prevent the network load fromrapidly varying when the actual data transmission is started, and thesynchronization deviation can be prevented from occurring when theactual data transmission is started.

FIG. 9 is a view illustrating an example of the time trend of thetransmission data volume via the network in the present embodiment. Thehorizontal axis indicates the time and the vertical axis indicates thetransmission data volume (Mbps). The time t0 to t1 is a transmissiontime of the test data, at this time the synchronization packet istransmitted along with the test data, and the synchronizing process isexecuted.

When the synchronization is established at time t2 in the slaveapparatus, thereafter it proceeds to the transmission time of the actualdata.

During the test data transmission period, the transmission data volumevia the network is small compared to the actual data transmissionperiod, but it is possible to reduce the difference with respect to thetransmission data volume at the time of the actual data transmission bythe test data transmission. In other words, it is possible to executethe synchronizing process in an environment similar to that of thesubstantial actual data transmission. Furthermore, the test data may bethe data having a stable data volume in order to decrease the jitter.Specifically, data with a little variation such as still image data,black image data and color bar data, or audio data with a littlevariation, text data or the like may be used as the test data.

5. With Regard to Other Embodiment

Next, other embodiment of the synchronizing process according to theprocess of the present disclosure will be described with reference toFIG. 10. FIG. 10 is a view illustrating a configuration example of aspecific communication system. Three video cameras 301 to 303 aredisposed at different positions, respectively, and for example, captureimages of a soccer game played in a soccer stadium. The images arecollected to a communication apparatus A310 in the stadium side.

Three video streams captured by three video cameras 301 to 303 are inputto the communication apparatus A310. The communication apparatus A310transmits them to a communication apparatus B330 via a network 320 bysetting the time stamp according to the clock embedded in thecommunication apparatus A310 with respect to the three video streams.

In such a communication system, it is necessary to execute the clocksynchronizing process between the communication apparatus A and thecommunication apparatus B. The synchronizing process can be executed asthe process according to the first embodiment or the second embodimentpreciously described. Hereinafter, a third embodiment different from thefirst and second embodiments will be further described.

In the third embodiment, the transmitting process of the test data inthe step S304 of the flow illustrated in FIG. 8 in the second embodimentpreviously described is executed as a transmission step of multipledifferent data volumes. A transmitting process example of the specifictest data will be described with reference to FIG. 11.

FIG. 11 is the same view as FIG. 9 previously described, and a viewillustrating an example of the time trend of the transmission datavolume via the network according to the present embodiment. Thehorizontal axis indicates the time, and the vertical axis indicates thetransmission data volume (Mbps). The period of time t0 to t2 is thetransmission period of the test data, the synchronization packet istransmitted along with the test data during this period, and thesynchronizing process is executed.

In the present embodiment, only an image captured by one cameraillustrated in FIG. 10, such as a video camera 301 is transmitted fromthe communication apparatus A310 to the communication apparatus B330 viathe network 320 during the test data transmission period of the time t0to t1. The camera image transmission period for the one camera is set asa first test data transmission period, and the synchronizing process isexecuted by transmitting the synchronization packet from thecommunication apparatus A310 to the communication apparatus B330.

At the time (t1), if the synchronization establishment is successful inthe communication apparatus B330 for example, the communicationapparatus B330 transmits the notification packet denoting thesynchronization establishment to the communication apparatus A310. Ifthe notification packet denoting the synchronization establishment isreceived from the communication apparatus B330, next, the communicationapparatus A310 enters the second test data transmission period, andtransmits the images captured by the two cameras as the test data. Forexample, the images captured by the video camera 301 and the videocamera 302 illustrated in FIG. 10 are transmitted from the communicationapparatus A310 to the communication apparatus B330 via the network 320.The camera image transmission period of the two cameras is set as asecond test data transmission period, and a second synchronizing processis executed by transmitting the synchronization packet from thecommunication apparatus A310 to the communication apparatus B330.

At the time (t2), if the synchronization establishment is successful inthe communication apparatus B330, the communication apparatus B330transmits the notification packet denoting the synchronizationestablishment to the communication apparatus A310. If the notificationpacket denoting the synchronization establishment is received from thecommunication apparatus B330, the communication apparatus A310 startsthe actual data transmission by finishing the test data transmissionperiod.

The images captured by the three cameras are transmitted in the actualdata transmitting process.

In this manner, at the time of the test data transmitting process, thesynchronizing process is continuously executed by progressivelyincreasing the transmission data via the network, thereby enabling astable and secure synchronizing process to be smoothly executed.

FIG. 12 is a flowchart describing the processing sequence of the clocksynchronizing process according to the third embodiment. For example, itis the flowchart describing the processing sequence according to thethird embodiment executed in the communication apparatus A310 and thecommunication apparatus B330 illustrated in FIG. 10.

Furthermore, the communication apparatus A310 and the communicationapparatus B330 illustrated in FIG. 10 have the same configurations asthe master apparatus 110 and the slave apparatus 120 illustrated in FIG.1 previously described. The process according to the flow illustrated inFIG. 12 is executed in each data processing unit in the master apparatus110 and the slave apparatus 120 illustrated in FIG. 1, for example. Forexample, the program in which the processing sequence according to theflow illustrated in FIG. 12 is recorded is obtained from the memory, andthe process is executed by executing the process according to theprogram obtained in the CPU of the data processing unit. Hereinafter,the process of each apparatus of the flow illustrated in FIG. 12 will bedescribed.

(Step S401)

First, the data processing unit of each communication apparatus whichexecutes the synchronizing process activates the software which is theprogram executing the synchronizing process in step S401.

(Step S402)

Next, in step S402, the data processing unit activates each apparatuswhich executes the process necessary for executing the synchronizingprocess, such as the network processor configuring the communicationunit.

(Step S403)

Next, in step S403, the activation setting of the network for executingthe communication between the master and the slave is performed.Specifically, the process enabling the communication between the masterand the slave, such as the communication setting according to thecommunication program and the process obtaining the communicationaddress, is executed. The processes of these steps S401 to S403 are thesame processes as the steps S201 to S203 of the flow of the firstembodiment previously described with reference to FIG. 6.

(Step S404)

The process of step S404 is the same test data transmission process asthe step S304 in the flow of the second embodiment previously describedwith reference to FIG. 8. However, in the present embodiment, the testdata transmission process is divided into other multiple circlings to beexecuted. In other words, the process in which the data volume isprogressively increasing is executed. First, in the first stage, aminimum data volume such as the data captured by one camera istransmitted as the test data.

(Step S405)

In step S405, the synchronization packet transmission and reception arestarted along with the test data transmission. For example, the processis the synchronizing process accompanied by the synchronization packettransmission and reception between the master and the slave previouslydescribed with reference to FIG. 3. For example, one of the twocommunication apparatuses is the master apparatus and the other is theslave apparatus, and the synchronization packet is transmitted from themaster apparatus to the slave apparatus. As previously described withreference to FIG. 3, for example, the synchronization packettransmission of 64 packets per second is performed from the masterapparatus to the slave apparatus.

(Step S406)

In step S406, the slave apparatus performs the control for synchronizingthe clock of the slave apparatus with the clock of the master apparatusby using the time information on the synchronization packet or the likereceived from the master apparatus. This process is executed as theprocess according to the algorithm specified in the IEEE1588 previouslydescribed with reference to FIGS. 1 to 3, for example. If it isdetermined that the synchronization is established in the slaveapparatus side, the notification packet denoting the synchronizationestablishment is transmitted from the slave apparatus to the masterapparatus. The master apparatus confirms the successful synchronizationestablishment by receiving the notification packet. If the confirmationis made, the determination process of the step S406 is “Yes”, and thenthe process proceeds to step S407.

(Step S407)

In step S407, it is determined whether or not the test data volumereaches the maximum test data volume specified in advance.

For example, in the example described with reference to FIG. 11, thetest data volume is the data captured by two cameras.

At this time, since the synchronization is established under thetransmission of the data captured by one camera only, the determinationof step S407 is “No”, and the process proceeds to step S408.

(Step S408)

In step S408, a test data increasing process is executed. For example,in the example described with reference to FIGS. 1 and 11, the processwhich sets the image data captured by the two cameras as the test datais executed.

(Steps S404 to S406)

Then, the synchronizing process of the steps S404 to S406 is executedunder the test data transmission of the two cameras.

This process corresponds to the process of the time (t1) to (t2) in theexample illustrated in FIG. 11. If the synchronizing process succeedsunder the network environment in which the image data captured by thetwo cameras is set as the test data in the step S406, the processproceeds to the step S407.

(Step S407)

In the step S407, it is determined whether or not the test data volumereaches the most test data volume specified in advance.

At this time, the synchronization is established under the transmissionof the data captured by the two cameras, it is determined that the testdata volume reached the most test data volume specified in advance, andthe process proceeds to step S409.

(Step S409)

In step S409, the transmission of the actual data to be substantiallytransmitted and received between the communication apparatuses isstarted. For example, in the example illustrated in FIG. 10, the processis started which transmits the image, the audio which are contentscaptured by the three video cameras 301 to 303, and three pieces ofstream data including other data from the communication apparatus A310to the communication apparatus B330.

In the present embodiment, in this manner the synchronizing processaccompanied by the synchronization packet transmission and reception isexecuted along with the test data transmission, and the process whichprogressively increases the transmission data volume of the test data isexecuted. This process can prevent the synchronization deviation due tothe rapidly increased network load when the actual data transmission isstarted.

Furthermore, as an example of the test data increasing process, theexample is described in which the process increasing the stream numberof the image captured by the camera is executed, however, in anotherembodiment, the test data may be set to be increased. For example, it ispossible to set the following items.

(1) The test data volume is increased from the data coded with a highcompression ratio to the data coded with a progressively loweredcompression ratio.

(2) The data volume is gradually increased by changing a samplingprocess of the camera capturing image.

(3) In an initial stage, SD image data is transmitted as the first testdata, and in the second stage, HD image data is transmitted as thesecond test data.

(4) In the initial stage at the time of transmitting the test data, cullrate of the transmission packet is highly set, and the cull rate islowered at the time of transmitting the second half of the test data,thereby gradually allowing the cull rate to be even the actual data istransmitted.

For example, in the setting described above, it is possible to set so asto gradually increase the transmission data volume at the time oftransmitting the test data. In addition, the increasing of thetransmission data volume during the test data transmission period is notlimited to a stepwise increasing process as illustrated in FIG. 11, andfor example, a smooth increasing process may be set as illustrated inFIG. 13. In addition, as illustrated in FIG. 14, when the actual datatransmission is started after the test data transmission period iscompleted, the progressively increasing the transmission data volume maybe set. For example, this process is the process in which the data witha high compression ratio is transmitted in the initial stage of the testdata transmission and thereafter the data with a progressively loweredcompression ratio is transmitted, or the SD image data is transmitted inthe initial stage of the actual data transmission, and thereby thisprocess can be realized by switching the SD image to the HD image aftera certain period of time.

In addition, in the embodiment described above, the example of thesynchronization establishment process is described before the actualdata transmission is started, however, after the actual data istransmitted, similarly even in a case where resynchronization isperformed, first of all, non-transmission period of the actual data isset by stopping the transmission of the actual data which is substantialtransmission data, such as the image, the audio and the data, thesynchronization is established after returning to the situation having alittle jitter by reducing the network load, and again, the process inwhich the transmission of the actual data (the image, the audio and thedata) is restarted may be executed.

In addition, the transmission of the actual data (the image, the audioand the data) is not completely stopped, the number of the images andthe audio being transmitted is reduced, and the data transmission amountof the network is decreased, thereby re-establishing the synchronizationtherebetween, and thereafter, the process which restarts thetransmission of the image, the audio, and the data may be performed. Inaddition, a codec rate of the actual data (the image, the audio data orthe like), in other words, the coding rate during the transmission isdecreased, and the data transmission amount of the network is reduced,thereby re-establishing the synchronization therebetween, andthereafter, the setting such as restarting the transmission of theimage, the audio and the data may be performed.

6. Summary of Configuration of Present Disclosure

As described above, with reference to a specified embodiment, theembodiments of the present disclosure are described in detail. However,in a scope without departing from gist of the present disclosure, it isapparent that those skilled in the art can make modification andsubstitution of the embodiment. In other words, the present disclosureis disclosed in an exemplary form, and it should not be interpreted to alimited extent. In order to determine the gist of the presentdisclosure, the scope of the claims should be referred.

Furthermore, a technology disclosed in the present specification cantake following configurations.

(1) A communication apparatus includes a data processing unit thatexecutes a clock synchronizing process between a host apparatus and acommunication partner apparatus; and a communication unit that executesa communication with the communication partner apparatus, wherein thedata processing unit executes the clock synchronizing processaccompanied by a synchronization packet transmission and reception withthe communication partner apparatus during a non-transmission period ofactual data scheduled to be transmitted to the communication partnerapparatus, and wherein the data processing unit starts an actual datatransmission with respect to the communication partner apparatus aftersynchronization is established by the clock synchronizing process.

(2) The communication apparatus according to (1), wherein the dataprocessing unit executes the clock synchronizing process accompanied bythe synchronization packet transmission and reception with thecommunication partner apparatus before the actual data transmissionstarts, and wherein the data processing unit executes the actual datatransmission with respect to the communication partner apparatus afterthe synchronization is established by the clock synchronizing process.

(3) The communication apparatus according to (1) or (2), wherein thedata processing unit temporarily stops the actual data transmissionafter the actual data transmission starts, wherein the data processingunit executes the clock synchronizing process accompanied by thesynchronization packet transmission and reception with respect to thecommunication partner apparatus during a temporary stop period of theactual data transmission, and wherein the data processing unit restartsthe actual data transmission with respect to the communication partnerapparatus after the synchronization is established by the clocksynchronizing process.

(4) The communication apparatus according to (1) to (3), wherein thedata processing unit starts the actual data transmission under acondition that a notification packet denoting synchronizationestablishment is received from the communication partner apparatus.

(5) The communication apparatus according to (1) to (4), wherein thedata processing unit executes a data transmission and reception processonly for a packet used for a synchronizing process applied to the clocksynchronizing process during an execution period of the clocksynchronizing process.

(6) The communication apparatus according to (1) to (4), wherein thedata processing unit transmits and receives a packet used for asynchronizing process applied to the clock synchronizing process and atest data packet storing test data during an execution period of theclock synchronizing process.

(7) The communication apparatus according to (6), wherein the dataprocessing unit sequentially increases a data volume of the test dataduring the execution period of the clock synchronizing process.

(8) The communication apparatus according to (6) or (7), wherein theactual data is configured by a plurality of items of image data capturedby a plurality of cameras, and wherein the data processing unit usespartial items of the captured image data selected from the plurality ofitems of image data captured by the plurality of cameras, as the testdata.

(9) The communication apparatus according to (1) to (8), wherein theactual data is data in which image data is included.

(10) The communication apparatus according to (1) to (9), wherein theactual data is data in which a time stamp is set.

(11) The communication apparatus according to (1) to (10), wherein thedata processing unit executes the clock synchronizing process accordingto a sequence specified in IEEE1588.

(12) A communication apparatus includes a data processing unit thatexecutes a clock synchronizing process between a host apparatus and acommunication partner apparatus; and a communication unit that executescommunication with the communication partner apparatus, wherein the dataprocessing unit executes the clock synchronizing process accompanied bya synchronization packet transmission and reception with thecommunication partner apparatus during a non-reception period of actualdata scheduled to be received from the communication partner apparatus,and wherein the data processing unit starts an actual data receptionfrom the communication partner apparatus after synchronization isestablished by the clock synchronizing process.

(13) The communication apparatus according to (12), wherein the dataprocessing unit starts the actual data reception after a notificationestablishment denoting a synchronization packet is transmitted withrespect to the communication partner apparatus.

(14) The communication apparatus according to (12) OR (13), wherein thedata processing unit executes a data transmission and reception processonly for a packet used for a synchronizing process applied to the clocksynchronizing process during an execution period of the clocksynchronizing process.

(15) The communication apparatus according to (12) OR (13), wherein thedata processing unit transmits and receives the packet used for asynchronizing process applied to the clock synchronizing process and atest data packet storing test data during an execution period of theclock synchronizing process.

(16) A communication system includes a first communication apparatus;and a second communication apparatus that executes communication withthe first communication apparatus, wherein the first communicationapparatus executes a clock synchronizing process accompanied by asynchronization packet transmission and reception with the secondcommunication apparatus during a non-transmission period of actual datascheduled to be transmitted to the second communication apparatus,wherein the second communication apparatus executes the clocksynchronizing process to which a synchronization packet is appliedduring a non-reception period of the actual data, and transmits anotification packet denoting synchronization establishment to the firstcommunication apparatus after synchronization is established, andwherein the first communication apparatus starts an actual datatransmission with respect to the second communication apparatusaccording to notification packet reception from the second communicationapparatus.

(17) A first apparatus, including:

at least one processor programmed to:

communicate first data between the first apparatus and second apparatusvia a network;

communicate, while at least a portion of the first data is beingcommunicated via the network, a synchronization packet between the firstapparatus and the second apparatus; and

communicate second data between the first apparatus and the secondapparatus after synchronization between the first apparatus and thesecond apparatus has been established.

(18) The first apparatus of (17), wherein communicating first databetween the first apparatus and the second apparatus comprisestransmitting the first data from the first apparatus to the secondapparatus.

(19) The first apparatus of (17), wherein communicating first databetween the first apparatus and the second apparatus comprises receivingthe first data by the first apparatus from the second apparatus.

(20) The first apparatus of (17), wherein communicating thesynchronization packet between the first apparatus and the secondapparatus comprises transmitting the synchronization packet from thefirst apparatus to the second apparatus.

(21) The first apparatus of (17), wherein communicating thesynchronization packet between the first apparatus and the secondapparatus comprises receiving the synchronization packet by the firstapparatus from the second apparatus.

(22) The first apparatus of (17), further including:

receiving an indication that synchronization between the first apparatusand the second apparatus has been established; and

wherein the communicating the second data is performed in response toreceiving the indication.

(23) The first apparatus of (17), wherein the first data is image data.

(24) The first apparatus of (17), wherein communicating the first databetween the first apparatus and the second apparatus comprisescommunicating the first data using a substantially stable data volume.

(25) The first apparatus of (17), wherein communicating the first databetween the first apparatus and the second apparatus comprisescommunicating the first data using multiple different data volumes.

(26) The first apparatus of (25), wherein communicating the first datausing multiple different data volumes comprises communicating the firstdata using a first substantially stable data volume for a first periodof time and communicating the first data using a second substantiallystable data volume for a second period of time after the first period oftime, wherein the first substantially stable data volume and the secondsubstantially data volume are different.

(27) The first apparatus of (25), wherein communicating the first datausing multiple different data volumes comprises communicating the firstdata using a variable data volume that increases during a time periodduring which at least a portion of the first data is communicated.

(28) The first apparatus of (17), wherein communicating the second datacomprises communicating the second data using a first data volume thatincreases to a second data volume over a predetermined period of time.

(29) The first apparatus of (17), wherein communicating thesynchronization packet comprises communicating the synchronizationpacket in accordance with a clock synchronization processing sequencespecified in IEEE 1588.

(30) The first apparatus of (17), wherein the at least one processor isfurther programmed to:

halt communication of the second data between the first apparatus andthe second apparatus;

re-establish synchronization between the first apparatus and the secondapparatus; and

resume communication of the second data between the first apparatus andthe second apparatus after synchronization between the first apparatusand the second apparatus has been re-established.

(31) The first apparatus of (17), wherein the second data iscommunicated between the first apparatus and the second apparatus usinga first data volume, and wherein the at least one processor is furtherprogrammed to:

reduce the first data volume of the second data communicated between thefirst apparatus and the second apparatus to a second data volume;

re-establish synchronization between the first apparatus and the secondapparatus; and

resume communication of the second data between the first apparatus andthe second apparatus at the first data volume after synchronizationbetween the first apparatus and the second apparatus has beenre-established.

(32) The first apparatus of (17), wherein communicating thesynchronization packet between the first apparatus and the secondapparatus comprises initiating a communication of the synchronizationpacket at a point in time after at least a portion of the first data iscommunicated between the first apparatus and the second apparatus.

(33) A first apparatus, including:

a network interface configured to communicate with a second apparatusvia a network; and

at least one processor programmed to:

transmit first data to the second apparatus via the network interface;

communicate, while at least a portion of the first data is beingtransmitted, a synchronization packet between the first apparatus andthe second apparatus via the network interface; and

transmit second data to the second apparatus after synchronizationbetween the first apparatus and the second apparatus has beenestablished.

(34) A first apparatus, including:

a network interface configured to communicate with a second apparatusvia a network; and

at least one processor programmed to:

receive, via the network interface, first data sent from the slaveapparatus;

communicate, while at least a portion of the test data is being receivedvia the network interface, a synchronization packet between the firstapparatus and the second apparatus; and

receive second data from the second apparatus after synchronizationbetween the first apparatus and the second apparatus has beenestablished.

(35) A method of synchronizing a clock of a first apparatus and a clockof a second apparatus in communication with the first apparatus via anetwork, the method including:

transmitting first data from the first apparatus to the second apparatusvia the network;

communicating, while at least a portion of the first data is beingtransmitted, a synchronization packet between the first apparatus to thesecond apparatus via the network; and

transmitting second data from the first apparatus to the secondapparatus after synchronization between the first apparatus and thesecond apparatus has been established.

(36) A method of synchronizing a clock of a first apparatus and a clockof a second apparatus in communication with the first apparatus via anetwork, the method including:

receiving, by the first apparatus, first data sent from the secondapparatus via the network;

communicating, while at least a portion of the first data is beingreceived, a synchronization packet between the first apparatus and thesecond apparatus via the network; and

receiving second data from the second apparatus after synchronizationbetween the first apparatus and the second apparatus has beenestablished.

Further, a processing method of executing in the above-describedapparatus and the system, or the program executing the process is alsoincluded in the configuration of the present disclosure.

In addition, a series of processes described in the specification can beexecuted by hardware, software or a combination configuration of both.When the process is executed by the software, the program in which theprocessing sequence is recorded is executed by being installed in thememory built into a dedicated hardware in a computer, or it is possibleto execute by installing the program in a general-purpose computer inwhich various processes can be executed. For example, the program can berecorded in advance in a recording medium. Besides being installed fromthe recording medium to the computer, the program is received via anetwork such as LAN (Local Area Network) or the internet, and can beinstalled in the recording medium such as an embedded hard disc.

Furthermore, various processes described in the specification may notonly be executed in time series according to the description, but may beexecuted in parallel or individually according to a processingcapability of the apparatus executing the process or when necessary. Inaddition, the system in the present specification is a logicalcollection configuration of multiple apparatuses, and the apparatus ofeach configuration is not limited to those within the same housing.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2012-136457 filed in theJapan Patent Office on Jun. 16, 2012, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

INDUSTRIAL APPLICABILITY

As described above, according to the configuration of the embodiment ofthe present disclosure, an efficient clock synchronizing process isrealized between the communication apparatuses via the network.Specifically, the clock synchronizing process is executed as followsbetween the first communication apparatus and the second communicationapparatus which communicate via the network. In other words, the firstcommunication apparatus executes the synchronizing process accompaniedby the synchronization packet transmission and reception with the secondcommunication apparatus, during the non-transmission period of theactual data such as the image contents to be transmitted to the secondcommunication apparatus. The second communication apparatus executes theclock synchronizing process to which the synchronization packet isapplied during the non-reception period of the actual data, and afterthe synchronization is established, the notification packet indicatingthe synchronization establishment is transmitted to the firstcommunication apparatus. The first communication apparatus starts thetransmission of the actual data such as the image contents with respectto the second communication apparatus, depending on the notificationpacket received from the second communication apparatus. Thisconfiguration enables the synchronizing process to be executed in astable situation with less network load and less network delayfluctuation (the jitter).

REFERENCE SIGNS LIST

-   110 Master apparatus-   111 Master clock-   112 Counter-   113 Data processing unit-   114 Communication unit-   115 Master clock signal-   120 Slave apparatus-   121 Slave clock-   122 Counter-   123 Data processing unit-   124 Communication unit-   125 Slave clock signal-   301 to 303 Video camera-   310 Communication apparatus A-   320 Network-   330 Communication apparatus B

The invention claimed is:
 1. A first apparatus, comprising: at least oneprocessor configured to: communicate multiple first data at multipledifferent data volumes between the first apparatus and a secondapparatus via a network; communicate, while at least a portion of eachof the multiple first data is communicated via the network, respectiveones of multiple synchronization packets between the first apparatus andthe second apparatus; and communicate second data between the firstapparatus and the second apparatus after synchronization between thefirst apparatus and the second apparatus has been established based onthe multiple synchronization packets.
 2. The first apparatus of claim 1,wherein the communication of the multiple first data between the firstapparatus and the second apparatus comprises transmission of themultiple first data from the first apparatus to the second apparatus. 3.The first apparatus of claim 1, wherein the communication of themultiple first data between the first apparatus and the second apparatuscomprises reception of the multiple first data by the first apparatusfrom the second apparatus.
 4. The first apparatus of claim 1, whereinthe communication of the multiple synchronization packets between thefirst apparatus and the second apparatus comprises transmission of themultiple synchronization packets from the first apparatus to the secondapparatus.
 5. The first apparatus of claim 1, wherein the communicationof the multiple synchronization packets between the first apparatus andthe second apparatus comprises reception of the multiple synchronizationpackets by the first apparatus from the second apparatus.
 6. The firstapparatus of claim 1, wherein the at least one processor is furtherconfigured to receive an indication that the synchronization between thefirst apparatus and the second apparatus has been established; andwherein the communication of the second data is based on receipt of theindication.
 7. The first apparatus of claim 1, wherein the multiplefirst data is image data.
 8. The first apparatus of claim 1, wherein thecommunication of the multiple first data between the first apparatus andthe second apparatus comprises communication of the multiple first dataat a stable data volume.
 9. The first apparatus of claim 1, wherein thecommunication of the multiple first data at multiple different datavolumes comprises communication of test data at a first stable datavolume for a first period of time and communication of the test data ata second stable data volume for a second period of time after the firstperiod of time, wherein the first stable data volume and the secondstable data volume are different.
 10. The first apparatus of claim 1,wherein the communication of the multiple first data at multipledifferent data volumes comprises communication of test data at avariable data volume that increases in a time period within which atleast a portion of the test data is communicated.
 11. The firstapparatus of claim 1, wherein the communication of the respective onesof multiple synchronization packets comprises communication of themultiple synchronization packets based on a clock synchronizationprocess sequence specified in IEEE
 1588. 12. The first apparatus ofclaim 1, wherein the at least one processor is further configured to:halt communication of the second data between the first apparatus andthe second apparatus; re-establish the synchronization between the firstapparatus and the second apparatus; and resume communication of thesecond data between the first apparatus and the second apparatus afterthe synchronization between the first apparatus and the second apparatushas been re-established.
 13. The first apparatus of claim 1, wherein thesecond data is communicated between the first apparatus and the secondapparatus at a first data volume, and wherein the at least one processoris further configured to: reduce the first data volume of the seconddata communicated between the first apparatus and the second apparatusto a third data volume; re-establish the synchronization between thefirst apparatus and the second apparatus; and resume communication ofthe second data between the first apparatus and the second apparatus atthe first data volume after the synchronization between the firstapparatus and the second apparatus has been re-established.
 14. Thefirst apparatus of claim 1, wherein the communication of the respectiveones of multiple synchronization packets between the first apparatus andthe second apparatus comprises initiation of a communication of therespective ones of multiple synchronization packets at a point in timeafter at least a portion of each of the multiple first data iscommunicated between the first apparatus and the second apparatus. 15.The first apparatus of claim 1, wherein the communication of the seconddata comprises communication of the second data at a first data volumethat increases to a second data volume over a period of time.
 16. Afirst apparatus, comprising: a network interface configured tocommunicate with a second apparatus via a network; and at least oneprocessor configured to: transmit multiple first data to the secondapparatus via the network interface at multiple different data volumes;communicate, while at least a portion of each of the multiple first datais transmitted, respective ones of multiple synchronization packetsbetween the first apparatus and the second apparatus via the networkinterface; and transmit second data to the second apparatus aftersynchronization between the first apparatus and the second apparatus hasbeen established based on the multiple synchronization packets.
 17. Afirst apparatus, comprising: a network interface configured tocommunicate with a second apparatus via a network; and at least oneprocessor configured to: receive, via the network interface, multiplefirst data sent from the second apparatus at multiple different datavolumes; communicate, while at least a portion of each of the multiplefirst data is received via the network interface, respective ones ofmultiple synchronization packets between the first apparatus and thesecond apparatus; and receive second data from the second apparatusafter synchronization between the first apparatus and the secondapparatus has been established based on the multiple synchronizationpackets.
 18. A method, comprising: synchronizing a first clock of afirst apparatus and a second clock of a second apparatus incommunication with the first apparatus via a network, the synchronizingcomprising: transmitting multiple first data from the first apparatus tothe second apparatus via the network at multiple different data volumes;communicating, while at least a portion of each of the multiple firstdata is transmitted, respective ones of multiple synchronization packetsbetween the first apparatus to the second apparatus via the network; andtransmitting second data from the first apparatus to the secondapparatus after synchronization between the first apparatus and thesecond apparatus has been established based on the multiplesynchronization packets.
 19. A method, comprising: synchronizing a firstclock of a first apparatus and a second clock of a second apparatus incommunication with the first apparatus via a network, the synchronizingcomprising: receiving, by the first apparatus, multiple first data sentfrom the second apparatus via the network at multiple different datavolumes; communicating, while at least a portion of each of the multiplefirst data is received, respective ones of multiple synchronizationpackets between the first apparatus and the second apparatus via thenetwork; and receiving second data from the second apparatus aftersynchronization between the first apparatus and the second apparatus hasbeen established based on the multiple synchronization packets.